In recent years, inter-wiring distances in a semiconductor device are becoming increasingly shorter as elements of the semiconductor device are downscaled. When the inter-wiring distance becomes shorter, the inter-wiring capacity becomes larger. This tendency causes signal delay or an increase in power consumption. To reduce such inter-wiring capacity, it is considered to adopt a low-dielectric-constant film (Low-k film) as a material of an interlayer dielectric film or to increase the thickness of the interlayer dielectric film.
To this end, it is effective to further reduce the dielectric constant of the Low-k film by making the Low-k film porous. However, a porous film is possibly excessively etched in an etching process because an etching rate of the porous film is high. That is, the porous film is difficult to control in the etching process.
Meanwhile, if the thickness of the interlayer dielectric film is increased, the aspect ratio of contact holes is also increased, and the embeddability of a metallic material such as aluminum is deteriorated. When the embeddability is low, it generates voids in contact plugs, which increases contact faults between wirings. A material such as tungsten, which has good embeddability, can be used as the metallic material. However, if tungsten, which is higher than aluminum in cost, is used as the metallic material, it disadvantageously increases the manufacturing cost of semiconductor devices.